This cross-sectional study of juvenile rheumatoid arthritis (JRA) patients and healthy controls will measure total body & axial bone mineralization in both prepubertal (5-11 year old males & females) and postpubertal (females at least 24 months post menarche) subjects. In addition, variables known to be important in bone mineralization will be quantitated such as dietary intake, physical activity, serum/urinary minerals and calciotropic hormones, serum cytokines, fractional calcium absorption utilizing stable isotopes, vitamin D receptor pleomorphisms, and severity of articular inflammation will be measured.